This invention relates to a perpendicular magnetic recording disk to be mounted in a HDD (hard disk drive) of a perpendicular magnetic recording system, a disk substrate for a perpendicular magnetic recording medium, which is for use in manufacturing the perpendicular magnetic recording disk, and methods of manufacturing the perpendicular magnetic recording disk and the disk substrate for a perpendicular magnetic recording medium.
Recently, rapid advancement of the information society requires information recording apparatus or devices having a much higher information recording capacity. For example, in a magnetic recording apparatus such as a HDD (hard disk drive), an information recording capacity exceeding 60 Gbyte is required for a 2.5-inch magnetic disk.
For the purpose of complying with such requirement, it is necessary to realize the information recording density exceeding 100 Gbit per one square inch (100 Gbit/inch2) in the magnetic disk. In order to perform stable recording/reproducing operations at such high recording density, it is preferable to use a perpendicular magnetic recording system as a magnetic recording/reproducing system.
In order to obtain a magnetic disk adapted to the perpendicular magnetic recording system (which will hereinafter be called a “perpendicular magnetic recording disk”), it is required to adopt a design concept drastically different from a magnetic disk for the in-plane magnetic recording system which is widely used at present.
For example, a substrate and a recording medium adapted to the perpendicular magnetic recording system are proposed in Japanese Patent Application Publication (JP-A) No. 2001-143245.
The perpendicular magnetic recording disk is structured as a double-layer perpendicular magnetic recording medium in which a magnetic underlayer comprising a soft magnetic layer and a perpendicular magnetic recording layer comprising a hard magnetic layer are formed on a substrate. With this structure, stable recording/reproducing operations can be realized within a high recording density region.
Herein, the soft magnetic layer means a layer made of a soft magnetic substance (i.e., a magnetic substance exhibiting a soft magnetic property) while the hard magnetic layer means a layer made of a hard magnetic substance (i.e., a magnetic substance exhibiting a hard magnetic property).
Generally, the hard magnetic layer is used as the perpendicular magnetic recording layer. In the double-layer perpendicular magnetic recording medium, the soft magnetic layer helps a magnetic head to record a signal in the perpendicular magnetic recording layer comprising the hard magnetic layer. In this connection, in order to constitute a suitable magnetic circuit through the magnetic head, the perpendicular magnetic recording layer, and the hard magnetic layer in the double-layer perpendicular magnetic recording medium, the soft magnetic layer must have a large thickness.
On the other hand, in order to improve the recording/reproducing characteristics of the magnetic recording medium at a high recording density, it is necessary to heat the substrate and to deposit the perpendicular magnetic recording layer on the substrate which has been heated. However, since the soft magnetic layer has the large thickness as described above, a substrate temperature drops during deposition of the perpendicular magnetic recording layer. As a consequence, the high recording density of the perpendicular magnetic recording disk is difficult to achieve.
For the purpose of solving such a problem, it is proposed to heat the substrate after forming the soft magnetic layer and before forming the perpendicular magnetic recording layer. In this method, however, the property of the soft magnetic layer is often degraded by heating. In this event, it is difficult to obtain a desired effect.
In the double-layer perpendicular magnetic recording medium, the soft magnetic layer must be thick as described above. This results in another problem that the production cost of the magnetic disk is increased.
Specifically, it is assumed to use a single-substrate/disk deposition apparatus (fixed target deposition apparatus), which is typically used in a magnetic disk production process. In this event, in order to obtain a suitable thickness of the soft magnetic layer, it is required to perform deposition by the use of a plurality of deposition apparatus connected in series or by the use of a large number of deposition chambers connected to one another because the thickness of the soft magnetic layer is large. Therefore, an increased number of steps and an increased amount of materials become necessary.
On the other hand, an in-plane magnetic recording medium widely used at present can be produced by the use of a single deposition apparatus. Therefore, the production cost of the perpendicular magnetic recording medium becomes extremely high as compared with the production cost of the in-plane magnetic recording medium. For this reason, market penetration of the perpendicular magnetic recording disk is prevented.